1. Field of the Invention
The present invention relates to panels and methods for manufacturing the same, and more particularly relates to liquid crystal panels formed with liquid crystal layers by a one-drop fill method.
2. Description of the Related Art
Process steps for manufacturing a liquid crystal panel include the process step of charging a liquid crystal material into a panel. Methods for charging a liquid crystal material into a panel include a dip method and a dispenser method. In these methods, the following technique is used: A pair of substrates are bonded to each other with a sealant interposed therebetween, then a liquid crystal material is charged through an opening of the sealant into a panel by utilizing capillarity and a differential pressure, and then the opening is sealed. However, with an increase in the screen size, the cycle time for charging a liquid crystal material into a panel is becoming longer.
In recent years, a one-drop fill method (alternatively, referred to as an ODF method or a drop bonding method) has been developed as another method for charging a liquid crystal material into the panel. In the one-drop fill method, while an opening is not formed in a seal pattern formed on one of a pair of substrates to be bonded to each other later, a liquid crystal material is dropped to the inside of the seal pattern, then the other substrate is superimposed on the substrate on which the seal pattern is placed to surround the liquid crystal material under a reduced pressure, and then a sealant is cured. Use of the one-drop fill method allows an increase in the screen size and a dramatic reduction in the cycle time for charging a liquid crystal material into a panel.
However, in the one-drop fill method, an uncured sealant has been in contact with a liquid crystal material until the sealant is cured, leading to the possibility of components of the sealant leaking into a liquid crystal layer. This may cause an unstable orientation of liquid crystal and cause spotting, unevenness and flicker, resulting in reduced display quality of a liquid crystal panel.
Techniques for preventing contact between an uncured sealant and a liquid crystal material in a one-drop fill method have been disclosed in Japanese Unexamined Patent Application Publication Nos. 6-194615; 2002-40442; 2003-315810; and 2004-233648. More particularly, these documents disclose that when a seal barrier is arranged to extend along the side of a sealant near a liquid crystal layer, this prevents contact between an uncured sealant and a liquid crystal material.
However, use of this method increases the number of process steps for forming a seal barrier, resulting in an increase in production cost.
Meanwhile, for a panel with a narrow frame, such as a mobile panel, a light-shielding layer (black matrix) is formed around a display region of the panel without being spaced apart from the edge of the display region in order to reduce the area of a non-display region of the panel as much as possible. FIG. 7(a) is a plan view schematically illustrating a mobile liquid crystal panel, FIG. 7(b) is a schematic enlarged view of a portion of a TFT (thin film transistor) substrate 100 surrounded by Y in FIG. 7(a), and FIG. 7(c) is a schematic enlarged view of a portion of a color filter substrate 200 surrounded by Y in FIG. 7(a). As illustrated in FIG. 7(c), the color filter substrate 200 is provided at its region corresponding to a sealant 300 with a black matrix 500. Therefore, the sealant 300 needs to be cured by applying light, e.g., ultraviolet light, through the TFT substrate 100, opposed to the color filter substrate 200, to the sealant 300.
Various lines 400 are formed on an end portion of the TFT substrate 100. For this reason, when light (ultraviolet light) is applied through the TFT substrate 100 to the sealant 300, the lines 400 shade the sealant 300 from the light so that the sealant 300 is partially prevented from sufficiently undergoing photopolymerization. In other words, since light (ultraviolet light) has conventionally been able to be applied only through the TFT substrate 100 to the sealant 300, the sealant 300 shaded from the light by the lines 400 for the TFT substrate 100 has not been able to be sufficiently cured. Therefore, use of the sealant 300 containing both a photocuring (ultraviolet-curing) agent and a thermal curing agent has had to achieve both ultraviolet curing and thermal curing of the sealant 300.
Meanwhile, once a decrease in the viscosity of the sealant 300 has been caused by the application of heat for thermal curing, curing will proceed, resulting in an increase in the viscosity thereof. In this process, the liquid crystal temperature increases and consequently exceeds the nematic-isotropic phase transition temperature (NI point). Therefore, before the sealant 300 is sufficiently cured, impurities in the sealant 300 may leak into a liquid crystal layer.